A longitudinal field experiment of the influence of peer groups on the motives, attitudes, and behavior of delinquents while they are in correctional institutions and after they are released. Brings together theories of inmate social organization and the social psychology of small group influence in order to discover determinants of the strength, direction (relative to correctional goals) and enduringness of peer group influence over institutionalized youth. Expects some findings to differ from those reports in the standard literature on group influences, because of the fact of involuntarism inherent in correctional institutions. Studies small residential youth groups in three institutions that utilize variants of a treatment program especially designed to enlist peer influence to achieve individual reform. Takes advantages of the natural differences from among the groups and the treatments they are given, and of the randomness that occurs naturally in the assignment of youth to groups to create quasi-experimental research design. Utilizes questionnaire, interview, archival, and observational measures. Aims to extend social psychological knowledge of group influence to degrees of values (such as coerciveness of group membership) heretofore unavailable to researchers; and to improve the effectiveness of correctional efforts.